Process for the production of butadiene



Patented Dec. 18,1945- I raocnss FOR 'rn'E PRODUCTION o BUTADIENE Charles E. Ayn-es, Phillips,

, lips Petroleum Company,

ware

Tex., assignor to Phila corporation of Dela- Application May "I, 1943, Serial No. 486,032

12 Claims. 260-680) will be apparent tothose skilled in the art from This invention relates to a process for the production of butadiene. More particularly, it relates to the production of butadiene'from cyclohexane by an improved process.

That butadiene may be produced from cyclohexane is known to those skilled in the art. of butadiene production. It is known that butadiene may be produced in this manner by .contacting the cyclohexane with a hot contact body, as aluminum silicates heated to a dark red color. Butadiene has been produced also by passage of cyclohexane through 'a quartz tube heated to 1200 F.

The present invention provides an improved process for producing butadiene from cyclohexane. By means of the invention, a high yield of butadiene may be obtained, the reaction is readily carried out in commercial apparatus, and the reaction may be carefully controlled. The cracking operation may be performed at optimum temperature and with optimum residence time at the cracking temperature to produce a maximum yield of the desired product.

In' the pyrolytic decomposition of organic compounds it is often true that the greatest amount of the desired product is formed at higher temperatures. It is also true that at these higher temperatures the reaction time orresidence time is very short, being in the order of seconds or fractions of seconds. With the conventional methods of heating a considerable interval of time is spent in raising the temperature of the compound to the desired level. During this interval of time the cracking reaction is taking place at temperatures other than the most eflicient, resulting in the production volume of undesirable products; In the method set forth by this invention where the compound to be'cracked is injected in a relatively small volume into a large volume of gas already heated to or above the desired temperature, the tem-' perature of the compound to be cracked is raised .almost instantaneously to the proper level enabling the reaction to take place at the temperature proper for maximum production.

vAn object of this invention is to provide an improved process for the production of butadiene.

A further object of this invention is to provide an improved process for cracking ,cyclohexane to produce butadiene. 1

Another object of this invention is to provide a process for simultaneous cracking'bi propane of too great a and cyclohexane to form valuable hydrocarbon products.

Other objects and advantages of this invention a consideration of the following detailed descrip tion andthe accompanying drawing.

Figure 1 is a diagrammatic elevation of an apparatus suitable for carrying out the process of the present invention. 1

Figure 2 is a plan view of apparatus suitable for use with the process of the invention showing a reaction zone in the form of a coil of tubing with points of entry of the various fluids.

Inacoordance with the present invention, the cyclohexane to be cracked is injected into a stream of fluid, inert to or beneficial to theformation of butadiene, at or near the reaction temperature. This is carried out by heating the stream of fluid to'about the reaction temperature, injecting cyclohexane into the stream, maintaining the temperature for the optimum reaction time, and cooling the ,mixture below the reaction temperature at the end of said reaction time. In this manner possible to raise the temperature of the hexane quickly from a value below the decomposition temperature to a temperature within the range at which decomposition or cracking occurs. -The cyclohexane is mixed in this manner with a moving streamof the carrier fluid. By

correlation of the volume of the reaction zone with the rate of flowtherethrough, the reaction time may be carefully controlled. Satisfactory methods of making these correlations under the variable conditions which'exist in actual operaing furnace 'l of conventional design. From the in which the propane is preheated, the propane passes to the radiant sections 8A and 8B of the furnace for cracking andthen passes to the soaking coil 9 maintained at about the reaction temperature conducive to the conversion of propane and cyclohexane to the desired decomposition products.

Cyclohexane is passed through line Ii to the heating coil I! where it is preheated to an elevated temperature somewhat below the reaction temperature. The preheated cyclohexane is carried' by aconduit l3 to the valves MA, MB and MC through which it maybe admitted to the reaction zone, soaking coil 9, entering the zone at any of various points alOngitS length. The cyclohexane upon mixingwith the propane and convection section,

its decomposition products in the soaking coil is almost instantly heated to its decomposition temmain'at that temperature for the proper interval before cooling. The most desirable point of inperature. The reaction time may be controlled carbons resulting from the cracking. The separation of desirable products from this mixture will depend of course upon its composition and various other factors evident to those skilled in the art. The various steps involved in the separations are more or less conventional and the selection of the proper steps becomes a matter of engineering and economics. Forthe purpose of this invention it is necessary only to indicate the separation system diagrammatically. For simplification, also, only the more important components of the effluent have been indicated on the drawing although any degree of separation may be made in practice. A recycle stream comprising unconverted cyclohexane is passed through line l8 to line l3 for recycling into the reaction zone. Benzene may be separated from the effluent and withdrawn from the separation zone through line i 9 from which it may be passed to a hydrogenation step '20 for reconversion to cyclohexane. The cyclohexane thus formed is recycled to the reaction zone for further conversion to butadiene. The butadiene' formed is withdrawn from the separation system through line 22 through which it passes to storage. further purification, or disposal. The residual hydrocarbons, i. e. the components which make up the balance of the effluent are passed through line 24 to suitable disposal means.

With reference to, Figure 2 of the drawing, pip ing of a conventional tubestill heater is shown illustrating the points of introduction of cyclohexane to the tubing coil. The coil 25 may represent any or all of the various heating sections 6, 8A, 8B, and 9 of Figure 1. The carrier fluid, for example a fluid comprising propane is introduced to the coil 25 at the inlet 26. This fluid is heated to' a temperature at or slightly above that required for the cyclohexane cracking. Fluid comprising cyclohexane is introduced at any or all of the points of injection represented by the numerals 21A, 21B, and 21C which correspond to the inlets controlled by valves MA, MB, and C, respectively, of Figure 1. The coolant, from pipe l of Figure 1, may be introduced to the coil at or near the furnace outlet 28 through the inlet 29.

A large volume of gas, vapor, or liquid carrier fluid is fed to the furnace coil at the inlet 26. The character of this feed stock may be inert or active: 1. e., if the process is designed solely for the purpose of cracking thecompound to be inJected, the feed stock may be inert but, if it is desired to process the feed, some. such stock as an organic compound may be used. The feed stock passes through the furnace coil and is heated to the-proper reaction temperature. The cyclohexane is introduced into the furnace coil at one of the injection inlets 21A, 21B, and2'IC.

The desirable point of injection is determined by design and calculation and is the point where the cyclohexane will be raised almost instantaneously to the optimum reaction temperature and will rejection may be at inlet 210 near the furnace outlet or, if more residence time is desired may fall at inlets 21A or 213. The ratio of carrier fluid to cyclohexane usually wlll'be high to provide suflicient heat inertia to withstand the thermal shock of the addition of the injected cyclohexane.

Cyclohexane may be cracked or decomposed with the production of butadiene at temperatures within the range of 1100 to 1500 F.; with the present invention the higherportion of this temperature range may be most satisfactorily employed. The preferred temperatures used in the process of this invention are within the range of 1300 to 1500 F., suitably about 1400 F. Nearatmospheric or low superatmospheric pressures may be advantageously employed. Pressures of about atmospheric to about pounds per square inch gage are suitable. Yields comparable to those obtained heretofore at subatmospheric pressures may be obtained by the process of the present invention at atmospheric or low super- The advantages attendating pressures in contrast to operations requiring subatmospheric pressures are known to and apparent to those skilled-in the art.

The preferred reaction time is within the range of about 0.1 to about 2 seconds. A reaction time of about 0.5 second has been found very satisfactory. The shorter reaction times may be used when temperatures near the upper limit c the temperature range are employed, while Ja ger reaction times are required for optimum yields when lower temperatures are employed. By correlating the various operating conditions, butadiene yields of about 30 weight percent may be obtained from the cyclohexane cracked. The yield is increased when the benzene formed in the cracking step is hydrogenated and recycled. The total yield may be increased by about 4. to

5 weight percent by hydrogenation of the ben-' the process is not limited thereby and other relatively inert or beneficial fluids may be employed. The hydrocarbons of low molecular weight are preferred, as for example paraflins and olefins of one to five carbon atoms per molecule. Thermal decomposition of the carrier fluid may advantageously take place, as in the case of propane illustrated herein, with the formation of valuable products. By this means the apparatus employed in preheating and carryin out the cyclohexane cracking serves a double purpose which is highly advantageous. A further advantage of such combination of two reactions is that the same separation equipment may be used to separate like components formed in the two reactions. For example, ethylene formed in the cracking of propane and in the cracking of cyclohexane may be removed from the eflluent of the reaction zone in a single separation step.

The products of the cyclohexane cracking comprise hydrogen, methane, butadiene, and various other saturated and unsaturated hydrocarbons as will be evident from the examples.

' fluid'to 1 gas volume of carrier passed through the coil at a yield from the cyclohexane -rier fluid is passed thereof is about Various amounts or carrier fluid may be used; the ratio of carrier fluid to cyclohexane may be of gas volumes of carrier fluid for each About 4 gas volumes of carrier fluid to ,each gas volume of cyclohexane has been ,found satisfactory when using propane asthe carrier fluid as indicated. The coolant used may be the sameas gas volume the carrier fluid or maybe any fluid inert to the products of the reaction. Cooled eiiiuent may employed as coolant fluid for injection at the furnace outlet or any of the components of the be advantageously emuent may be advantageously employed, as for example liquid propane and butane.

' Exnurm I A continuous salt bath maintained at 1402 F. Propane was clohexane feed stock comprising about 80 weight percent cyclohexane was vaporized and injected into the propane stream at a. point in the coil about two thirds of the distance from the propane inlet to the ei'iiuent outlet. The flow rates of propane and cyclohexane were so correlated with the relative volumes of the two zones in the coil as to approximate a 3 to 1 mol ratio of propane tothe cyclohexane feed stock. The cyclohexane feedstock analysis was as follows:

f Li uid Component vogime g:

' perc t n-Hexane 3. 3i 1 Me-cyciopentane 4. i4 4. 0e 1soheptanes. 11.81 10.62 Cyclohexen'e 80. 74 82. 44

The pressure was substantially atmospheric with a residence time in the coil of 2.26 seconds for propane and 0.57 second for cyclohexane, the

constant rate. Cy-

coil was immersed in a molten Propane ma stock (carrie fluid) Component Total Cyclohezane feed stock Component LbJday' CycloheXane 71. Paraflins I 18,000 Total 00.000

Uneonyerted cyclohexane, together with some. unsaturated Cs hydrocarbons and some C1 andheavier hydrocarbons, is recycled to the point of introduction of cyclohexane. recycle is as follows:

Recycle The analysis 01 the for separation into various desirable fractions including a fraction comprising the butadiene produced and a fraction making up the recycle pr pane having aresidence 0f seconds stream 'rhe analy is of the emuent is as fol- P ior to introduction or the cyclohexane teed. w I r, The composition of the total eiliu'ents was 08-45 ,Eflluent follows: v

I Component LbJdey Moi Weight I Component percent percent M no: 000 112.10 25.51 13.58 Bill 1. 2a72 2100 Egg 3.82 3.81 am as? 13.74 0 m 0.10 13.31 .700 am 1144 .200 an 1.84 m 0.11 v 0.33 m 000 iti fi-asessv til 31w Y m oasens'ai saa': 1.200 0.72 zoo cr-Qlhydrocalbons 4,000 0.27 o, Heavier hydrocarbons 2,35 w 580,400

Of the butadiene formed, 1.2 weight percent is attributable to the propane. The butadiene I feed is, therefore, 5.51 weight percent or a yield 01329.8 weight percent based on the cyclohexane cracked. 4

Exam. II

225,000 1b./da'y of a propane feed stock as carthrough a mrnaoe o! the type of the drawing. The total residence time or the propane and products 2 seconds. The propane feed stock is heated to about1400 F. at a pressure or about 15 ounds per square inch gaze and shown in Figure 1 About 30 weight percent conversion of cycloa ll low thatoi the carrier fluid, admi't'ing the cycle" obtained. About 1,000 lbi/day in the-range of l fluid per volume of cyclohexane such that the temperatureof the resulting mixture is substantially instantaneously brought within the rangeof 1100 to 1500 F., holding the resulting mixture at a temperature within said range for a period of time within the range of 0.1 to 2 secfrom cyclohexane which comprises heating a hydrocarbon carrier fluid to a temperature above about 1300 but not above about 1500 F.; admixing cyclohexane at a temperature below its decomposition temperature with said carrier fluid at said temperature in proportions within the range of 1 to 10 voliunes of said carrier fluid per volume of cyclohexane and thereby effecting substantially instantaneous heating of the cyclohexane from a temperature below its decomposition temperature to a temperature within the range of about 1300 to about 1500 F., holding the resulting mixture at a temperature within said range for a period of time within the range of about 0.1 to 2 seconds sumcient to effect conversion of said cyclohexan to butadiene, 'cooling the resultant mixture, and separating butadiene therefrom.

3. A process for the production of butadiene from cyclohexane which comprises passing a hydrocarbon carrier fluid through a closed elongated reaction zone formed by a heating coil at a pressure within the range of about atmospheric to about 100 pounds per square inch gage and at an elevated temperature such that the carrier fluid is brought to a temperature above about 1300 but not above about 1500 F., admixing cyclohexane with said carrier fluid by injecting same into said zone adjacent the end thereof in proportions within the range of 1 to 10 volumes of said carrier fluid per volume of cyclohexane such that the temperature of the resultant mixture is substantially instantaneously brought within the range of 1300 to 1500 mixture at a temperature within said range for a period of time within to 2 seconds suflicient to effect conversion of said cyclohexane to butadiene, cooling the resulting eilluent of said zone, and separating the butadiene therefrom. i

4. A process for the production of butadiene from cyclohexane which comprises passing a hydrocarbon carrier fluid through a closed elongated reaction zone of restricted cross-section and having a fluid inlet tained at near-atmospheric pressure and an elevated temperature such that the temperature of said fluid is above about 1100 and not above about R, injecting along said reaction zone cyclohexane into admixture with said carrier fluid in F., holding the resulting.

and a fluid outlet and main-' hexane with the carrier fluid in proportions with-:- to 10 volumes of said carrier 7 eflluent of said zone hexane into said stream in said reaction zon in proportions within the range of 1 to 10 volumes of propane per volume of cyclohexane such that the cyclohexane in the resulting mixture is substantially instantaneously brought to a temperature within the range of 1100 to 1500 F., maintaining the resulting mixture at a temperature within said range for a period of time said cyclohexane to butadiene, cooling the resulting eflluent of said zone, and separating butadiene therefrom.

6. A process for the production of butadiene from cyclohexane which comprises heating propane to a temperature above about 1300 but not above 1500 F. at a pressure in the range of about atmospheric to about 100 pounds per square inch gage, injecting a hydrocarbon fluid comprising chiefly cyclohexane into said propane in proportions within the range of 1 to 10 volumes of pro- I pane per volume of said hydrocarbon fluid such to butadiene, cooling the resulting reaction prod- I the range of about 0.1

proportions within the range of 1 to '10 volumes 01' said carrier fluid pervolume of cyclohexane such that the temperature of the resulting mixture is substantially instantaneously brought 01' about 1100 to about 1500 F.,

within the range the cyclohexane being admixed with the carrier fluid in the zone at such a point relative to th fluidoutlet thereof as to limit the residence time of the cyclohexane in said zone to a-period with- I in the range of 0.1 to 2 seconds, holding the resulting mixture -at a temperature within said range for said period to effect conversion of said cyclohexane to butadiene, cooling the resulting that the cyclohexane in the resulting mixture is immediately brought within the range of from ;about 1300 to about 1500 F., holding the resulting mixture at a temperature within said range for a period of time within the range of 0.1 to 2 seconds to effect conversion of said cyclohexane nets and separating butadiene therefrom.

7. A process for the production of butadiene from cyclohexane which comprises heating propane to a temperature above about 1300 but not above about 1500 F. effecting decomposition of -"a portion of the propane; heating cyclohexane to an elevated temperature below that at which appreciable decomposition of the cyclohexane takes place, injecting the so heated cyclohexane into the mixture resulting from said heating of said propane in proportions within the range of one to ten gas volumes of propane for each gas volume ofcyclohexane, the proportions being such that the temperature ofthe resulting mixture is substantially instantaneously brought within the range of about 1300 F. to about 1500 F., maintaining the mixture at a temperature within said range for a period of time, between about 0.1 to about 2seconds, suflicient to convert at least a portion of the cyclohexane to "butadiene, cooling said mixture at the end of said period to a temperature below that at which substantial decomposition of cyclohexane takes place, and separating the butadiene from said mixture.

8. A process for the production of butadiene -from cyclohexane which comprises passing a.

stream of propane through a closed elongated reaction zone of restricted cross-section at nearatmospheric pressure and at an elevated temperature. such that the propane is heated to a temperature above about 1300 but not above about 1500' part of the propane, irriecting a hydrocarbon fluid comprising cyclohexane into the propane decomposition mixture, the proportions of propane and cyclohexane-containing fluid 'being within the production of butadiene which comprises passing a H within the range of 0.1 to 2 seconds to efiect conversion of F. efl'ecting decomposition of at least the range of 1 to volumes of propane per volume of cyclohexane such that the temperature of the resulting mixture issubstantially instantaneously brought within the range of 1300 to 1500" F., the point of injection being so related to the outletof said zone as to limit the residence time of cyclohexane at said temperature to a period of time within the range of 0.1 to 2 seconds, cooling the eilluent of said zone to a temperature below that at which substantial decomposition of cyclohexane takes place, and separating the butadiene therefrom.

temperature at which it is cracked to butadiene,

eflecting said injection at a point in said coil located substantially ahead of the end of said coil and so Iocated that said propane stream has attained said first-mentioned temperature within the range of 0.1 to 2 seconds before reaching the end of said coil, flowing the resulting mixture through the remainder of said coil in said period of time which, will effect optimum cracking of cyclohexane to butadiene, quickly cooling the eflluent of said coil by admixture with coolant to a temperature below reaction temperature,

and treating the cooled efliuent to recover the butadiene content thereof. v

10. The process of claim 9 wherein said cracking temperature is within the range of 1300 to 1500 F., wherein said cracking is conducted at a pressure ranging from about atmospheric to about 100 pounds per square inch gage, wherein said period of tim is about 0.5 seconds, and wherein about 4 gas volumes of propane per gas volume of cyclohexane are employed.

11. The processof claim 9 including the further steps of recovering benzene from the eilluent, hydrogenating said benzene to cyclohexane and employing the resulting cyclohexane to gether with fresh cyclohexane froman outside source as said cyclohexane injected into said and that the cyclohexane so injected will be held at the cracking temperature for a period of time heated propane stream.

12. The process of claim 9 further characterized by the fact that said propane isat least partially converted to butadiene simultaneously with cracking of cyclohexane during passage through said coil, and that the butadiene so formed is recovered together with the butadiene derived from cracking of said cyclohexane.

CHARLES E. AYRES. 

